EFFECT OF HAEMATOCRIT ON THE PRIMARY-SECONDARY FLOW TRANSITION IN A ROTATIONAL RHEOMETER

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Abstract

Objectives: Literature suggests the shear-thinning rheology of blood delays laminar-turbulent transition but may not fully account for observations of this phenomena. This work investigates whether haematocrit levels also play a role, by testing their effect on primary-secondary flow transition in a rotational rheometer.

Methods: Tests used a rotational rheometer with 30mm radius (r) and 2° angle (α) cone, anticoagulated horse blood at 37°C, and Ht (25-65%) adjusted by centrifugation. Angular velocity (ω) was increased (1-100 rad/s, theoretical shear rate 0.1-1000 1/s ) to produce secondary flow and viscosity (μ) was measured. The modified Reynolds number was R=(r^2ωα^2ρ)/12μ. By fitting Sdougos’s empirical equation for cone-plate flow, combined with a Carreau viscosity model, effects of secondary flow and shear-thinning rheology on the relative (ratio of experimental to primary) torque were separated

Results: Horse blood showed shear-thinning behaviour, with zero-shear rate viscosities μ_0=6.41, 20.3, 40.3mPa.s and asymptotic viscosities μ_∞=2.45, 5.14, 6.74mPa.s for Ht=30, 42, 60% respectively. While greater than human blood, these are consistent with published horse data. An exponential increase in relative torque occurred for all Ht, indicating secondary flow. The values of R for which significant secondary flow occurred were R= 0.044, 0.13 and 0.24, for Ht=30, 42, 60% respectively.

Discussion and Conclusions: Even after accounting for differences in the shear-thinning viscosity, increasing Ht delayed transition from primary to secondary flow. This suggests the influence of RBCs on fluid dynamics goes beyond that of shear- thinning rheology, such as the Carreau model, and that RBCs “damp out” secondary velocity components.
Original languageEnglish
Pages (from-to)592-638
JournalThe International Journal of Artificial Organs
Volume44
Issue number9
Early online date6 Sep 2021
DOIs
Publication statusPublished - 30 Sep 2021
Event47th European Society for Artificial Organs Congress - Brunel University, London, UK United Kingdom
Duration: 7 Sep 202111 Oct 2021

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